It is understood that 22-year-old, Croatia-born Mitchell, who would be available on a free transfer, is currently training with Sky Bet Championship side Bolton Wanderers after spending last season playing for their under-23 side last season, but is not under contract for the upcoming campaign.
The defender began his career in New Zealand playing three seasons in the New Zealand Football Championship, two seasons with Wanderers SC, the club which he turned pro with in 2013, and one with WaiBOP United.
After opting to leave New Zealand in 2016, Adam signed a contract with Serbian giants Red Star Belgrade and was subsequently loaned out to OFK Beograd in a bid to gain some first-team football. After just eight loan appearances and no sign of football for Red Star he left the club and joined Slovenian side NK Celje.
Mitchell, who was among Walsall's tram to defeat Dutch giants Ajax on Thursday evening, was a regular member of Bolton's Under-23s last season and remains despite not being under contract part of their pre-season plans until a deal is reached.